Systems and methods for producing synthesis gas

ABSTRACT

The present invention relates to a system for producing synthesis gas comprising CO and H 2 . The system comprises a first gasification reactor and a second gasification reactor. The first one has an inlet for a first oxygen containing stream, an inlet for a first carbonaceous stream, and an outlet for raw synthesis gas produced in the first gasification reactor. The second one has an inlet for a second oxygen containing stream, an inlet for a second carbonaceous stream, and an outlet for raw synthesis gas produced in the second gasification reactor. A source of an oxygen containing stream is selectively connected to the inlet for the first oxygen containing stream of the first gasification reactor and to the inlet for the second oxygen containing stream of the second gasification reactor via a distributor.

CROSS REFERENCE TO AN EARLIER APPLICATION

Priority is claimed of European patent application No. 05106072.1 filed Jul. 5, 2005.

FIELD OF THE INVENTION

The present invention relates to systems and methods for producing synthesis gas comprising CO and H₂ from a carbonaceous stream using an oxygen containing stream.

BACKGROUND OF THE INVENTION

Generally in such systems and methods, a carbonaceous stream such as coal, brown coal, peat, wood, coke, soot, or other gaseous, liquid or solid fuel or mixture thereof, is partially combusted in a gasification reactor using an oxygen containing gas such as substantially pure oxygen or (optionally oxygen enriched) air or the like, thereby obtaining synthesis gas (CO and H₂), CO₂ and optionally a slag. In case where slag is formed during the partial combustion, it drops down and is drained through an outlet located at or near the reactor bottom.

The hot product gas, which may be referred to as raw synthesis gas, is typically quenched in a quench section which is located downstream of the gasification reactor. In the quench section a suitable quench medium such as water, cold gas, recycled synthesis gas or the like is introduced into the raw synthesis gas in order to cool it.

After the quenching, the raw synthesis gas is further processed, e.g. to remove undesired components from it or to convert the CO into methanol and various other hydrocarbons. The H₂ may be used a product gas or used for e.g. hydrocracking purposes.

WO-A-99/55618 describes a process to prepare a synthesis gas by means of two parallel-operated processes. One process is the partial oxidation, also referred to as gasification, of a biomass feed. In the parallel process, a natural gas is used as feed for a steam reforming process. Synthesis gas mixtures from both processes are combined.

WO-A-02/090250 describes a process to prepare a synthesis gas by means of two parallel-operated partial oxidation processes. In one process a solid or liquid feed is used as feed and in the parallel process a natural gas is used as feed. Synthesis gas mixtures from both processes are combined.

Known gasification reactors which operate on a liquid and especially on a solid feed, such as coal as in WO-A-02/090250, usually have a relative low availability. After a certain operating period, the reactor typically has to be shut down for a while, to check and repair the internals, if necessary. As a result no synthesis gas is produced for a while, or the syngas production is substantially halved as would be in the case of the process of WO-A-02/090250.

The above problem is even more pertinent in cases where the gasification reactor uses a particulate carbonaceous feed stream, such as coal and especially petroleum coke, that is intended to produce H₂ as the main product. If the gasification process is applied in a refinery environment, using petroleum coke as the feed to the gasification process, a high H₂ availability, usually greater than 98% of the year, and/or a high synthesis gas availability for generating power is desired. Hydrogen is used for the various refinery processes such as hydrotreating, hydrofinishing, hydrocracking and catalytic dewaxing. Disruptions in either the hydrogen or the power supply in a refinery is not desired. It is an object of the present invention to at least minimize the above problem.

It is a further object to provide a system ensuring a high availability of synthesis gas, while using as few components as possible.

It is an even further object to provide an alternative system for producing synthesis gas.

SUMMARY OF THE INVENTION

The present invention provides a system for producing synthesis gas comprising CO and H₂, the system comprising first and second gasification reactors.

The first gasification reactor may comprise a first-reactor oxygen inlet for a first oxygen-containing stream, a first-reactor fuel inlet for a first, carbonaceous stream, and a first-reactor outlet for raw synthesis gas produced in the first gasification reactor.

The second gasification reactor may comprise a second-reactor oxygen inlet for a second oxygen-containing stream, a second-reactor fuel inlet for a second carbonaceous stream, and a second-reactor outlet for raw synthesis gas produced in the second gasification reactor.

The system further comprises an oxygen source of an oxygen containing stream and a distributor for fluidly connecting the oxygen source to the first-reactor oxygen inlet and to the second-reactor oxygen inlet, the distributor being arranged to selectively connect the oxygen source to the first or second gasification reactor.

In another aspect the present invention provides a method of producing synthesis gas comprising CO and H₂, from a carbonaceous stream using an oxygen-containing stream, the method comprising at least the steps of:

-   (a) injecting a first carbonaceous stream and a first oxygen     containing stream into a first gasification reactor, the first     oxygen-containing stream originating from a source of oxygen; -   (b) at least partially oxidising the first carbonaceous stream in     the first gasification reactor, thereby obtaining a first raw     synthesis gas; -   (c) removing the first raw synthesis gas obtained in step -   (b) from the first gasification reactor; -   (d) injecting a second carbonaceous stream and a second     oxygen-containing stream into a second gasification reactor, wherein     the second oxygen containing stream originates from the source of     oxygen used in step (a); -   (e) at least partially oxidising the second carbonaceous stream in     the second gasification reactor, thereby obtaining a second raw     synthesis gas; -   (f) removing the second raw synthesis gas obtained in step (e) from     the second gasification reactor.

The first and second gasification reactors may function at the same time, but it is especially preferred that the first and second gasification reactors are used alternately.

The method may further comprise optional steps of:

-   (g) transporting the first synthesis gas removed in step (c) or the     second synthesis gas removed in step (f) to a shift converter; and -   (h) reacting at least a part of the CO in the first or second     synthesis gas transported in step (g) in the shift converter to     produce CO₂ and H₂.

The first carbonaceous stream may comprise a particulate carbonaceous stream which may comprise a petroleum coke.

The second carbonaceous feed may be a gaseous stream which may comprise at least one of the vacuum residue feed of the coking process and natural gas, preferably natural gas.

The invention further provides a method using a spare gasification reactor in a process to generate power from a source of petroleum coke in one or more parallel operated gasification reactors, which spare reactor is capable of preparing a spare synthesis gas mixture comprising carbon monoxide and hydrogen by partial oxidation of at least one of a vacuum residue and natural gas, using up to a maximum first volume of oxygen per hour as obtained from an air separation unit.

Power generation based on petroleum coke may then optionally be obtained by

-   (aa) partial oxidation of the petroleum coke using up to a maximum     second volume of oxygen per hour as obtained from the air separation     unit, to yield a synthesis gas mixture, -   (bb) using at least one of the synthesis gas mixture as obtained     from step (aa) and the optional spare synthesis gas mixture to     generate power.

Carbon dioxide may advantageously be isolated prior to the power generation in, for example, a gas turbine. Carbon dioxide may be subjected to sequestration or suitably used for agricultural uses or enhanced oil recovery.

Hydrogen may optionally be obtained in said preferred embodiment from the petroleum coke by

-   (aa1) partial oxidation of the petroleum coke using up to a maximum     second volume of oxygen per hour as obtained from the air separation     unit to yield a synthesis gas mixture, -   (bb1) subjecting at least one of the synthesis gas mixture as     obtained from step (aa1) and the optional spare synthesis gas     mixture to a water gas shift step to obtain shifted gas, -   (cc1) subjecting the shifted gas to a gas separation step to obtain     a hydrogen enriched mixture.

The gas separation step may comprise or consist of a pressure swing absorbing process (PSA).

Irrespective of whether power is generated and/or hydrogen produced, the maximum capacity of the air separation unit is preferably less than the sum of the maximum first and second oxygen volumes per hour.

The invention will hereinafter be illustrated by way of example in more detail with reference to the accompanying non-limiting drawing.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawing:

FIG. 1 schematically shows a process scheme for performing a method according the present invention.

For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line. Same reference numbers refer to similar components.

DETAILED DESCRIPTION

Reference is made to FIG. 1. FIG. 1 schematically shows a system 1 for producing synthesis gas.

The system 1 comprises a first gasification reactor 2, a second gasification reactor 3, an oxygen source 4 and a shift converter 5. In the embodiment shown in FIG. 1, the first gasification reactor 2 is a coal gasification reactor and the second gasification reactor 3 is a gas gasification reactor.

In the system 1 according to FIG. 1 a particulate coal containing stream 10 and an oxygen containing stream 60 are fed at inlets 6 and 7, respectively, into the coal gasification reactor 2.

Similarly, a gas containing stream 30 and an oxygen containing stream are 70 are fed into the gas gasification reactor 3 at inlets 9 and 11.

During normal use of the embodiment of FIG. 1 only the coal gasification reactor 2 is in function; the gas gasification reactor 3 functions as a spare unit for producing synthesis gas in case the coal gasification reactor 2 is out of order or on hot standby.

If the coal gasification reactor 2 is functioning, the oxygen source 4 feeds an oxygen containing stream 50 to the distributor 25 which selectively connects the source 4 to the coal gasification reactor 2 via lines 50 and 60. At this point no oxygen is fed to the gas gasification reactor 3.

The carbonaceous stream 10 is partially oxidised in the gasification reactor 2 thereby obtaining raw synthesis gas 20 (removed via outlet 8) and a slag (removed via stream 90). To this end usually several burners (not shown) are present in the gasification reactor 2.

The synthesis gas 20 produced in the coal gasification reactor 2 is usually fed to a quenching section (not shown); herein the raw synthesis gas is usually cooled.

As shown in the embodiment of FIG. 1, the synthesis gas 20 leaving the reactor 2 at outlet 8 is optionally further processed in a shift converter 5, to react at least a part of the CO to produce CO₂ and H₂, thereby obtaining a shift converted gas stream 80 which may be further processed or sold as such.

If desired, the synthesis gas stream 20 may be processed before entering the shift converter 5, e.g. in a dry solids removal unit (not shown) to at least partially remove dry ash in the raw synthesis gas 20. Also, the synthesis gas 20 may be fed to a wet gas scrubber (not shown).

If the coal gasification reactor 2 needs to be periodically checked, the gas gasification reactor 3 is started up (or is already on hot standby). The coal gasification reactor 2 is then shut down and the distributor 25 no longer feeds oxygen (via stream 60) to the coal gasification reactor 2, but connects the oxygen source 4 to the gas gasification reactor 3 via streams 50 and 70. The synthesis gas 40 removed from the gas gasification reactor 3 at outlet 12, may be processed similarly as the stream 20 and is also fed to the shift converter 5. In case a slag would be formed in the gasification reactor 3, a slag stream is removed via line 100.

According to an advantageous embodiment of the invention, the synthesis gas 40 is fed to the same shift converter 5 as stream 20 originating from the coal gasification reactor 2. Before stream 40 is fed to the same shift converter it is preferred to remove any solids from synthesis gas 20 in for example a separate dry solids removal step. Before stream 40 is fed to the same shift converter it is preferred to subject the synthesis gas to a separate wet gas scrubber. With “separate” is here meant, that when the spare second gasification reactor 3 is used the synthesis gas 40 does not pass the dry solids removal step and/or the wet gas scrubber used for stream 20.

As soon as the coal gasification reactor 2 is ready for use again, the coal gasification reactor 2 may be restarted. Then the distributor 25 may switch off the oxygen stream 70 to the gas gasification reactor 3, and oxygen is fed again through line 60 to coal gasification reactor 2. The gas gasification reactor 3 may then be shut down or for instance put on hot standby until later use. Thus, in the embodiment of FIG. 1 the reactors 2 and 3 are used alternately.

The person skilled in the art will readily understand that, if desired, the switching between the reactors 2 and 3 may proceed gradually. Thus, if the reactor 2 is to be shut down, the distributor 25 gradually decreases the oxygen stream 60 to reactor 2, at the same time increasing the oxygen stream 70 to reactor 3. As a result, the distributor 25 feeds oxygen to both reactors 2,3 at the same time for a certain period.

In the embodiment of FIG. 1 the system 1 may comprise an inlet for sulphur addition to sulfidise the catalyst being present in the shift converter 5. Hereby one and the same shift converter 5 can be used for the two different carbonaceous streams 10,30 (in this case, a “sour shift conversion” takes place in shift converter 5). Alternatively, a desulfurisation unit (not shown) may be present (thereby resulting in a “sweet shift conversion” in shift converter 5).

As the shift converter 5 is already known per se, it is not further discussed here in detail.

It has been contemplated that synthesis gas can be produced while ensuring a very high availability of the synthesis gas, even if the gasification reactor intended for the particulate carbonaceous stream is out of order.

Further it has been contemplated that the above may be achieved using a very simple system.

The combination of a gasification reactor intended for a particulate carbonaceous stream and a different type gasification reactor is contemplated more economic than if two gasification reactors intended for a particulate carbonaceous stream would be used which may be an important advantage.

The first and second gasification reactors may be any suitable reactor for partially oxidizing the respective carbonaceous stream. If desired more than one first and second gasification reactors may be used thereby obtaining a system comprising more than two gasification reactors being connected to the distributor.

The second gasification reactor may be used as a spare reactor, which may only be used if the first gasification does not operate, for example due to a failure to operate. In such an embodiment it is possible to limit the capacity of the air separation unit to a capacity, which is required to perform the gasification in the first gasification only. In case the first gasification fails, the second gasification can advantageously take over the preparation of synthesis gas, thereby making use of the oxygen manufacturing capacity, which is at that time not used by said first gasification reactor. As a result, the availability of synthesis gas may be ensured, even if the first gasification reactor or one of the first gasification reactors is out of order or on hot standby, while minimizing the required capacity of the oxygen manufacturing unit, suitably the air separation unit.

The first, particulate carbonaceous stream may be obtained from a high carbon containing feedstock such as naturally occurring coal, biomass or synthetic cokes. Synthetic coke is also referred to as petroleum coke. Petroleum coke is a by-product of a widely applied crude oil refining process. Petroleum coke may also be obtained as the by-product of a tar sands upgrading process as for example described in US-A-2002/0170846. In this publication a process is described wherein the heavy oil fraction of a bitumen or tar sands feed is converted into a gas oil product by means of a fluid coking process. Petroleum coke may for example be prepared by delayed coking, which is probably the most widely used coking process. Delayed coking uses a heavy residual oil as a feedstock. During delayed coking, heavy residual oil is introduced into a furnace, heated to about 480° C., and pumped into coking drums. The coking process initiates the formation of coke and causes it to solidify on the drum wall. Thermal decomposition drives off lower boiling products, which are removed continuously. When this reaction is complete, the drum is opened, and coke is removed. The first, particulate carbonaceous stream may be dry or wet. In the latter case the first stream is in the form of a slurry.

The first carbonaceous stream may also be a liquid stream. Suitable liquid streams are vacuum residues as obtained from crude mineral oils or tar sand oils or the asphalt fraction as obtained from a de-asphalting process using the vacuum residues as obtained from crude mineral oils or tar sand oil. Preferably the second carbonaceous stream is a gaseous stream as will be described below in case the first carbonaceous stream is such a liquid stream.

The second carbonaceous stream may be a substantially liquid or gaseous stream (or a combination of one or more thereof) suitable to be partially oxidized in the second gasification reactor, a gaseous stream being preferred. As a liquid stream e.g. oil, a condensate, a vacuum or atmospheric distillate or asphalt or other residue may be used.

The use of the vacuum residue feed of the coking process may be advantageous in situations wherein the coking operation itself fails to prepare the petroleum coke feed for the first gasification reactor. This will result in that the first gasification reactor fails to operate. The feed to the coking process may then be suitably used in the second gasification reactor.

As a gaseous stream for example natural gas, methane, ethane, propane, refinery gases, etc. may be used. Preferably the second carbonaceous stream is a gaseous stream, most preferably natural gas or mixtures of natural gas and refinery gasses, suitably refinery gasses comprising methane and ethane. A gaseous feed is preferred because the gasification reactor and the downstream gas processing steps may be of a more simple design. Furthermore the hydrogen to carbon monoxide molar ratio will be higher, resulting in less carbon dioxide by-product being made in the water shift reaction.

The source of an oxygen containing stream may be any suitable source. Preferably substantially pure oxygen or (optionally oxygen enriched) air or the like is used. Further, preferably a single source is used and is connected to both the first and the second gasification reactor(s). Preferably, the oxygen containing stream comprises >50 vol. % O₂, preferably >90 vol. % O₂, more preferably >95 vol. % O₂, even more preferably >99 vol. % O₂.

A preferred source of oxygen comprises a so-called air separation unit, wherein an oxygen containing stream can be prepared. Such air separation units and processes are well known and are also referred to as cryogenic air separation. In such a process compressed air is cooled and cleaned prior to cryogenic heat exchange and distillation into oxygen, nitrogen, and optionally, argon rich streams. Pressurizing these streams for delivery is accomplished by gas compression, liquid pumping or combinations of pumping followed by compression.

The maximum capacity of the air separation unit is preferably less than the sum of the oxygen requirements for gasification of the petroleum coke feed and the oxygen requirement for gasification of the natural gas feed as described above.

The capital investment for an air separation unit is very high. Thus processes, which require a lower oxygen capacity for the same synthesis gas production, are desired. In a preferred embodiment of the present invention the maximum capacity of the air separation unit is less than 80% of the sum of the oxygen requirements for the first and the second gasification reactor(s), especially if two first gasification reactors and one second gasification reactor are used. More preferably this percentage is less than 65%, especially when one first gasification reactors and one second gasification reactor are used. By definition the lower boundary for this percentage is 50%.

The person skilled in the art will readily understand that the distributor may have different embodiments as long as it is arranged to selectively connect the source of oxygen to the first or second gasification reactor.

With the term ‘raw synthesis gas’ is meant that this product stream may—and usually will—be further processed, e.g. in a dry solid remover, wet gas scrubber, a shift converter or the like.

The person skilled in the art will readily understand that the present invention may be modified in various ways without departing from the scope as defined in the claims. 

1. A system for producing synthesis gas comprising CO and H₂, the system comprising: a first gasification reactor comprising a first-reactor oxygen inlet for a first oxygen-containing stream, a first-reactor fuel inlet for a first, carbonaceous stream, and a first-reactor outlet for raw synthesis gas produced in the first gasification reactor; a second gasification reactor comprising a second-reactor oxygen inlet for a second oxygen-containing stream, a second-reactor fuel inlet for a second carbonaceous stream, and a second-reactor outlet for raw synthesis gas produced in the second gasification reactor; an oxygen source of an oxygen containing stream; and a distributor for fluidly connecting the oxygen source to the first-reactor oxygen inlet and to the second-reactor oxygen inlet, the distributor being arranged to selectively connect the oxygen source to the first or second gasification reactor.
 2. The system of claim 1, wherein the oxygen-containing stream comprises greater than 50 vol. % O₂.
 3. The system of claim 1, wherein the oxygen-containing stream comprises greater than 99 vol. % O₂.
 4. The system of claim 1, wherein the first carbonaceous stream is selected from the group consisting of a particulate and a liquid stream and the second carbonaceous stream is selected from a group consisting of a gaseous and liquid stream and a mixture thereof.
 5. The system of claim 1, wherein the first carbonaceous stream is a particulate stream.
 6. The system of claim 5, wherein the second carbonaceous stream is a gaseous stream.
 7. The system of claim 1, wherein the second carbonaceous stream is a gaseous stream.
 8. The system of claim 7, wherein the first carbonaceous stream is a liquid stream.
 9. The system of claim 1, wherein the oxygen source comprises an air separation unit having a maximum oxygen capacity of less than 80% of the sum of the oxygen requirements for the first and the second gasification reactors.
 10. The system of claim 9, wherein the maximum oxygen capacity of the air separation unit is less than 65% of the sum of the oxygen requirements for the first and the second gasification reactors.
 11. The system of claim 1, further comprising a second first gasification reactor.
 12. The system of claim 1, further comprising a shift converter being connected to the first-reactor outlet and the second-reactor outlet, in which shift converter at least a part of the CO in the synthesis gas may be reacted to produce CO₂ and H₂.
 13. A method of producing synthesis gas comprising CO and H₂, from a carbonaceous stream using an oxygen-containing stream, the method comprising the steps of: (a) injecting a first carbonaceous stream and a first oxygen containing stream into a first gasification reactor, the first oxygen-containing stream originating from a source of oxygen; (b) at least partially oxidising the first carbonaceous stream in the first gasification reactor, thereby obtaining a first raw synthesis gas; (c) removing the first raw synthesis gas obtained in step (b) from the first gasification reactor; (d) injecting a second carbonaceous stream and a second oxygen-containing stream into a second gasification reactor, and wherein the second oxygen containing stream originates from the source of oxygen used in step (a); (e) at least partially oxidising the second carbonaceous stream in the second gasification reactor, thereby obtaining a second raw synthesis gas; and (f) removing the second raw synthesis gas obtained in step (e) from the second gasification reactor; wherein the first and second gasification reactors are used alternately.
 14. The method of claim 13, wherein the oxygen containing stream comprises greater than 50 vol. % O₂.
 15. The method of claim 13, wherein the oxygen containing stream comprises greater than 99 vol. % O₂.
 16. The method of claim 13, wherein the first carbonaceous stream is selected from a group consisting of a particulate and a liquid stream and the second carbonaceous stream is selected from a group consisting of a gaseous and liquid stream and a mixture thereof.
 17. The method of claim 13, wherein the first carbonaceous stream is a particulate stream.
 18. The method of claim 17, wherein the second carbonaceous stream is a gaseous stream.
 19. The method of claim 13, wherein the second carbonaceous stream is a gaseous stream.
 20. The method of claim 19, wherein the first carbonaceous stream is a liquid stream.
 21. The method of claim 13, further comprising the steps of: (g) transporting at least one of the first synthesis gas removed in step (c) and the second synthesis gas removed in step (f) to a shift converter; and (h) reacting at least a part of the CO comprised in the at least one of the first and second synthesis gas transported in step (g) to produce CO₂ and H₂.
 22. A method using a spare gasification reactor in a process to generate power from a source of petroleum coke in one or more parallel operated gasification reactors, which spare reactor is capable of preparing a spare synthesis gas mixture comprising carbon monoxide and hydrogen by partial oxidation of at least one of a vacuum residue and natural gas, using up to a maximum first volume of oxygen per hour as obtained from an air separation unit, and wherein power is generated from the petroleum coke by (aa) partial oxidation of the petroleum coke using up to a maximum second volume of oxygen per hour as obtained from the air separation unit, to yield a synthesis gas mixture, (bb) using at least one of the synthesis gas mixture as obtained from step (aa) and the optional spare synthesis gas mixture to generate power wherein a maximum capacity of the air separation unit is less than the sum of the maximum first and second oxygen volumes per hour.
 23. The method of claim 22, further comprising a step of isolating carbon dioxide prior to the power generation.
 24. The method of claim 23, wherein the carbon dioxide is isolated in a gas turbine.
 25. The method of claim 22 carried out in the system of claim
 1. 26. A process to prepare hydrogen from a source of petroleum coke in one or more parallel operated gasification reactors employing a spare gasification reactor, which spare reactor is capable of preparing an optional spare synthesis gas mixture comprising carbon monoxide and hydrogen, by partial oxidation of at least one of a vacuum residue and natural gas, using up to a maximum first volume of oxygen per hour as obtained from an air separation unit, and wherein hydrogen is prepared from the petroleum coke by (aa1) partial oxidation of the petroleum coke using up to a maximum second volume of oxygen per hour as obtained from the air separation unit to yield a synthesis gas mixture, (bb1) subjecting at least one of the synthesis gas mixture as obtained from step (aa1) and the optional spare synthesis gas mixture to a water gas shift step to obtain shifted gas, (cc1) subjecting the shifted gas to a gas separation step to obtain a hydrogen enriched mixture, wherein the maximum capacity of the air separation unit is less than the sum of the maximum first and second oxygen volumes per hour.
 27. The process of claim 26, wherein the gas separation step comprises a pressure swing absorbing process.
 28. The process of claim 26 carried out in the system of claim
 1. 